VN hollow spheres assembled from porous nanosheets for high-performance lithium storage and the oxygen reduction reaction

The facile synthesis of well-defined hollow structures via a simple method remains a great challenge, especially for transition-metal nitrides (TMNs). Herein, we demonstrate a template-assisted strategy for the fabrication of VN hollow spheres (VN HSs) assembled from porous nanosheets. The resultant VN HSs have a hierarchical macroporous-mesoporous structure (the macropore size: 250 nm and the mesopore sizes: 5-30 nm), high surface area (66 m² g^-1), and uniform mesoporous shell with a thickness of 55 nm. The hierarchical porous structure is particularly beneficial for the mass transfer of reactant species. In view of these structural advantages, the VN HSs exhibit excellent lithium storage performance and high catalytic activity for the oxygen reduction reaction (ORR). Therefore, this work provides a promising approach for the design and synthesis of hierarchical porous nitrides with significantly enhanced performances in lithium-ion batteries and other electrochemical energy conversion and storage devices.